The present invention relates to polymer latex compositions useful in making elastomeric articles of manufacture, and more particularly composition useful in making an article of manufacture from a crosslinkable film having improved aging and ozone resistance properties, and other advantages over natural rubber.
Articles of manufacture such as gloves, condoms, bags, and the like are formed of latex polymeric materials, and are useful in a wide variety of applications relating to, for example, medical, industrial and household uses. These polymeric materials are generally water-based polymers which are readily formed using commercially-known processes. In such processes, it is important that the latex material be able to form a film on the surface of a mold. An example of such use relates to the making of latex gloves, especially for medical applications. Latex gloves are preferred since they can be made light, thin, flexible, tight-fitting, and substantially impermeable to a variety of li uids and gases. It is often desirable that the gloves possess ade uate physical properties such as tensile strength and elongation, and are comfortable to the wearer.
It is also desirable that the gloves possess ade uate aesthetic properties with respect to drape, softness, etc., provide a good barrier to microbial penetration, and be substantially odorless. A combination of high tensile strength and elongation combined with a low modulus is typically preferred. In addition to the above, it is desirable that the glove have sufficient snap or elastic recovery.
Conventional latex gloves have typically been formed of natural rubber primarily due to their resiliency, softness, ade uate physical properties, and good elastic recovery. Nonetheless, many wearers of such gloves are allergic to proteins found in natural rubber. These individuals often experience difficulty when wearing the gloves. As a result, there have been efforts to develop gloves made from synthetic materials which are comparable to the natural rubber gloves in terms of comfort and physical properties. One synthetic alternative focuses on using poly(vinylchloride) (PVC). PVC is typically plasticized in order to be pliable enough to use in glove applications. Gloves formed from PVC are undesirable in many respects. For example, the gloves do not possess a soft and rubbery feel. Furthermore, the plasticizer may migrate through the PVC and leach out when in contact with solvents. Also, it is believed that synthetic gloves formed from vinyl materials may provide an insufficient barrier to microbes due to imperfections in the film. Additionally, these gloves tend to display inade uate elastic recovery (snap) properties and poor softness.
Another possible alternative to gloves made of natural rubber is described in U.S. Pat. No. 5,014,362 to Tillotson et al. The Tillotson et al. patent proposes gloves made with elastomeric material which are claimed to possess ade uate physical properties relating to fluid permeability, strength, and resilience. The gloves are taught to be formed from a nitrile-containing rubber, more particularly a carboxylated nitrile containing butadiene rubber. Nitrile-containing rubber gloves are typically desirable in demanding end use applications, such as those which often re uire superior properties such as solvent and puncture resistance.
Another alternative is proposed in U.S. Pat. No. 5,910,533 to Ghosal et al. The Ghosal et al. patent proposes a latex composition for gloves having a relatively high (i.e. 80 to 99 percent by weight) amount of a conjugated diene monomer, and in addition includes an unsaturated acid monomer and an additional unsaturated monomer.
Although these various lattices provide articles of manufacture having high tensile strength and elongation properties, there continues to be a need for articles of manufacture having improved aging and resistance to ozone properties. There are also applications where the use of synthetic elastomers are desirable, but where the properties conferred by styrene, acrylonitrile or chloroprene or derivatives thereof are unnecessary or undesirable or both.
To these ends and other objects and advantages, the present invention provides a polymer latex composition. The latex composition comprises from about 35 to about 80 weight percent of aliphatic conjugated diene monomer; from about 10 to about 65 weight percent of unsaturated ester or amide monomer and, above 0 to about 15 weight percent of unsaturated acid monomer. By lowering the amount of the aliphatic conjugated diene monomer as compared to, for example, the amount proposed by Ghosal et al., improved aging and ozone resistance properties can result.
The latex in one embodiment is devoid of styrene, acrylonitrile and chloroprene and derivatives thereof. The latex can be formed into a crosslinked film, and utilized to manufacture a number of so-called xe2x80x9cdipped goodsxe2x80x9d such as articles including gloves, condoms, bags and the like. For example, the polymer latex can be contacted with a mold in the shape of the article and then cured to form the article. It is believed that high levels of conjugated diene monomers lead to high levels of residual unsaturation in the polymer chain which can result in undesirable properties such as poor aging and poor ozone resistance.
The present invention will now be described more fully hereinafter, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
The latex composition comprises from about 35 to 80 weight percent, preferably from about 45 to about 70 weight percent of aliphatic conjugated diene monomer, from about 10 to about 65 weight percent, preferably from about 20 to about 40 weight percent of unsaturated ester or amide monomer, and above 0 to about 15 weight percent, preferably about 2 to 7 weight percent of unsaturated acid monomer. Blends or copolymers of the monomers may be used.
Suitable conjugated diene monomers that may be used include, but are not limited to C4 to C9 dienes such as, for example, butadiene monomers such as 1,3-butadiene, 2-methyl-1,3-butadiene, and the like. Blends or copolymers of the diene monomers can also be used. A particularly preferred conjugated diene is 1,3-butadiene.
The unsaturated ester or amide monomers which may be used are well known and include, for example, acrylates, methacrylates, acrylamides and methacrylamides and derivatives thereof. The acrylic and methacrylic acid derivatives may include functional groups such as amino groups, hydroxy groups, epoxy groups and the like. Exemplary acrylates and methacrylates include, but are not limited to, various (meth)acrylate derivatives including, methyl methacrylate, ethyl methacrylate, butyl methacrylate, glycidyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, 3-chloro-2-hydroxybutyl methacrylate, 2-ethylhexl(meth)acrylate, dimethylaminoethyl(meth)acrylate and their salts, diethylaminoethyl(meth)acrylate and their salts, acetoacetoxyethyl(meth)acrylate, 2-sulfoethyl(meth)acrylate and their salts, methoxy polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, tertiarybutyl aminoethyl (meth)acrylate and their salts, benzyl(meth)acrylate, 2-phenoxyethyl(meth)acrylate, gamma-methacryloxypropyltrimethoxysilane, propyl(meth)acrylate, isopropyl(meth)acrylate, isobutyl (meth)acrylate, tertiarybutyl (meth)acrylate, isobornyl (meth)acrylate, isodecyl(meth)acrylate, cyclohexyl(meth)acrylate, lauryl(meth)acrylate, methoxyethyl (meth)acrylate, hexyl (meth)acrylate, stearyl(meth)acrylate, tetrahydrofufuryl(meth)acrylate, 2(2-ethoxyethoxy), ethyl(meth)acrylate, tridecyl(meth)acrylate, caprolactone(meth)acrylate, ethoxylated nonylphenol(meth)acrylate, propoxylated allyl(meth)acrylate and the like. Other acrylates include methyl acrylate, ethyl acrylate, butyl acrylate, glycidyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, and hydroxybutyl acrylate.
Exemplary (meth)acrylamide derivatives include, but are not limited to, acrylamide, N-methyolacrylamide, N-methyolmethacrylamide, 2-acrylamido-2-methylpropanesesulfonic acid, methacrylamide, N-isopropylacrylamide, tert-butylacrylamide, N-Nxe2x80x2-methylene-bis-acrylamide, N,N-dimethylacrylamide, methyl-(acrylamido) glycolate, N-(2,2 dimethoxy-1-hydroxyethyl) acrylamide, acrylamidoglycolic acid, alkylated N-methylolacrylamides such as N-methoxymethylacrylamide and N-butoxymethylacrylamide
Suitable dicarboxylic ester monomers may also be used such as, for example, alkyl and dialkyl fumarates, itaconates and maleates, with the alkyl group having one to eight carbons, with or without functional groups. Specific monomers include diethyl and dimethyl fumarates, itaconates and maleates. Other suitable ester monomers include di(ethylene glycol) maleate, di(ethylene glycol) itaconate, bis(2-hydroxyethyl) maleate, 2-hydroxyethyl methyl fumarate, and the like. The mono and dicarboxylic acid ester and amide monomers may be blended or copolymerized with each other.
Ester and amide monomers which may be used in the polymer latex composition also include, for example, partial esters and amides of unsaturated polycarboxylic acid monomers. These monomers typically include unsaturated di- or higher acid monomers in which at least one of the carboxylic groups is esterified or aminated. One example of this class of monomers is of the formula RXOCxe2x80x94CHxe2x95x90CHxe2x80x94COOH wherein R is a C1 to C18 aliphatic, alicyclic or aromatic group, and X is an oxygen atom or a NRxe2x80x2 group where Rxe2x80x2 represents a hydrogen atom or R group. Examples include, but are not limited to, monomethyl maleate, monobutyl maleate and monooctyl maleate. Partical esters or amides of itaconic acid having C1 to C18 aliphatic, alicyclic or aromatic groups such as monomethyl itaconate can also be used. Other mono esters, such as those in which R in the above formula is an oxyalkylene chain can also be used. Blends or copolymers of the partial esters and amides of the unsaturated polycarboxylic acid monomer can also be used.
A number of unsaturated acid monomers may be used in the polymer latex composition. Exemplary monomers of this type include, but are not limited to, unsaturated mono- or dicarboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, and the like. Derivatives, blends, and mixtures of the above may be used. Methacrylic acid is preferably used. Partial esters and amides of unsaturated polycarboxylic acids in which at least one carboxylic group has been esterfied or aminated may also be used.
In one embodiment, the latex composition is devoid of styrene, acrylonitrile, chloroprene and their derivatives. In accordance with another embodiment, the polymer latex composition may include additional monomers. The additional unsaturated monomer may be employed for several reasons. For example, the additional monomers may aid in processing, more specifically, help to reduce the time of polymerization of the latex. The presence of the additional unsaturated monomer may also help in enhancing the physical properties of a film, glove, or other article containing the polymer latex composition. A number of unsaturated monomers may be used and are well known to the skilled artisan. Examples include, but are not limited to, nitrile-containing monomers and aromatic monomers. Mixtures of the above may be used. The additional unsaturated monomer may be used from about 0 to about 15 percent based on the weight of the monomers. Nitrile-containing monomers which may be employed include, for example, acrylonitrile, fumaronitrile and methacrylonitrile. Blends and mixtures of the above may be used.
For the purposes of the invention, the term xe2x80x9caromatic monomerxe2x80x9d is to be broadly interpreted and include, for example, aryl and heterocyclic monomers. Exemplary aromatic vinyl monomers which may be employed in the polymer latex composition include styrene and styrene derivatives such as alpha-methyl styrene, p-methyl styrene, vinyl toluene, ethylstyrene, tert-butyl styrene, monochlorostyrene, dichlorostyrene, vinyl benzyl chloride, vinyl pyridine, vinyl naphthalene, fluorostyrene, alkoxystyrenes (e.g., p-methoxystyrene), and the like, along with blends and mixtures thereof.
The polymer latex composition may also include other components such as, for example, urethanes, epoxies, styrenic resins, acrylic resins, melamine-formaldehyde resins, and conjugated diene polymers (e.g., polybutadiene, styrene-butadine rubbers, nitrile butadiene rubbers, polyisoprene, and polychloroprene). Blends, derivatives, and mixtures thereof may also be used.
Conventional surfactants and emulsifying agents can be employed in the polymer latex composition. Polymerizable surfactants that can be incorporated into the latex also can be used. For example, anionic surfactants can be selected from the broad class of sulfonates, sulfates, ethersulfates, sulfosuccinates, and the like, the selection of which will be readily apparent to anyone skilled in the art. Nonionic surfactants may also be used to improve film and glove characteristics, and may be selected from the family of alkylphenoxypoly(ethyleneoxy)ethanols where the alkyl group typically varies from C7-C18 and the ethylene oxide units vary from 4-100 moles. Various preferred surfactants in this class include the ethoxylated octyl and nonyl phenols. Ethoxylated alcohols are also desirable surfactants. A typical anionic surfactant is selected from the diphenyloxide disulfonate family, such as benzenesulfonic acid, dodecyloxydi-, disodium salt. In addition to, or in place of the surfactants, a polymeric stabilizer may be used in the composition of the invention.
The polymer can include crosslinking agents and other additives, the selection of which will be readily apparent to one skilled in the art. Exemplary crosslinking agents include vinylic compounds (e.g., divinyl benzene); allyllic compounds (e.g., allyl methacrylate, diallyl maleate); and multifunctional acrylates (e.g., di, tri and tetra (meth)acrylates), sulfur, metal complexes, metal salts, and metal oxides (e.g., zinc oxide). Peroxides may also be used. Additional ingredients which may be used include, but are not limited to, chelating agents (e.g., ethylendiaminetetraacetic acid), dispersants (e.g., salts of condensed naphthalenesulfonic acid); buffering agents (e.g., ammonium hydroxide); and polymerization inhibitors (e.g., hydro uinone). Chain transfer agents (e.g., carbon tetrachloride, butyl mercaptan, bromotrichloromethane and t-dodecyl mercaptan) may also be used in the invention, preferably less than about 2 percent based on the weight of the monomers. More preferably, the chain transfer agent is used from about 0.0 to about 1.5 weight percent, and most preferably from about 0.3 to about 1.0 weight percent.
The monomers used in forming the polymer latex composition of the invention may be polymerized in a manner known to those who are skilled in the art. For example, the monomers may be polymerized at a temperature preferably between about 5xc2x0 C. and 95xc2x0 C., and more preferably between about 10xc2x0 C. and 70xc2x0 C.
The invention also relates to a crosslinked film formed from a polymer latex composition described herein. Numerous articles of manufacture can be formed from the crosslinked film and polymer latex composition according to the process of the invention. Such latex articles generally include those which are typically made from natural rubber and which contact the human body.
The films can be made into self-supported or form stable articles. The films are mechanically self-supporting without significant deformation, i.e., it can maintain its dimensions (e.g., length, thickness, circumference, etc.) against gravity without any exterior support such as a mold. It is recognized by those skilled in the art, the article could be supported, e.g., lined if additional support is desired. Exemplary articles of manufacture include, but are not limited to, gloves, condoms, medical devices, catheter tubes, bags, balloons, and blood pressure bags. Exemplary techni ues are described in U.S. Pat. No. 5,084,514 to Szczechura et al., the disclosure of which is incorporated by reference herein in its entirety.
Typically, the polymer latex composition is prepared by emulsion polymerization. The composition can be compounded with one or more crosslinkers (e.g., metal oxides such as zinc oxide, sulfur, and peroxides), along with antioxidants, fillers, and other ingredients. The compounding or mixing may be done in any suitable manner.
Similarly, the article of manufacture can be made in any suitable manner. For example, suitable forms or molds in the shape of a hand are heated in an oven, and are optionally immersed or dipped into a coagulant. A suitable coagulant includes, for example, a solution of a metal salt, preferably calcium nitrate, in water or alcohol. The form is then withdrawn from the coagulant, and the excess li uid is permitted to dry. As a result, a residual coating of coagulant is left on the form. The form coated with the coagulant is then immersed or dipped into the polymer latex composition of the present invention. The latex coagulates and forms a film on the form. The amount of time the form is immersed in the latex typically determines the thickness of the film. The longer the dwell time, the thicker the film.
The form is then removed from the latex, and is immersed in a water bath to remove the coagulant and some of the surfactant. The latex coated form is then placed in a drying oven at a temperature preferably between about 60xc2x0 C. and about 100xc2x0 to remove water from the film. When the film is dry, the mold is placed in a curing oven preferably at a temperature between about 100xc2x0 C. and 170xc2x0 C. for about 5 to about 30 minutes. If desired, the same oven can be used for drying and curing, and the temperature can be increased with time.
The cured glove is removed from the form. It may be powdered or postprocessed for ease of removal and for ease of donning. The glove preferably has a thickness ranging from about 3 mil to about 20 mil.
The crosslinked film and glove formed in accordance with the present invention may have various physical properties. Preferably, the above materials have a tensile strength of at least about 1000 psi, an elongation of at least about 300 percent, and a modulus at 100 percent elongation of no more than about 1000 psi. More preferably, the materials have a tensile strength of at least about 1400 psi, an elongation of at least about 400 percent, and a modulus at 100 percent elongation of no more than about 500 psi.
In addition to the above, the crosslinked film and article of manufacture produced in accordance with the invention can contain additional (at least a second) polymeric films in contact thereto so as to form composite structures. The application of the additional polymeric films may be achieved by techni ues which are known in the art. For example, the polymeric films may be formed on the crosslinked film and article by coating, spraying, or xe2x80x9coverdippingxe2x80x9d. The resulting materials may then be dried and cured in accordance with known and accepted techni ues. The additional polymeric films may be formed from a wide number of materials including, but not limited to, neoprene, nitrites, urethanes, acrylics, polybutadiene, polyisoprene, and the like. Mixtures of the above may also be used. The additional polymeric films may be present in a variety of configurations. For example, in one embodiment, an additional film may be positioned above the crosslinked film. In a second embodiment, an additional film may be positioned below the crosslinked film. In a third embodiment, the crosslinked film may be located between two additional films. The configurations of different films may be selected as desired by the skilled artisan.
The crosslinked film of the invention may be used in conjunction with other conventional materials, such as textile substrate which may be present in the form of an article such as a glove, for example. As an example, supported gloves are well known in the art. In this instance, the crosslinked film typically covers or is lined by the textile substrate, although other configurations are possible. For the purposes of the invention, the term xe2x80x9ctextilexe2x80x9d is to be broadly interpreted and may be formed from a variety of synthetic and natural materials such as, but not limited to, nylon, polyester, and cotton. Blends and mixtures thereof may also be used.